The conversion of sugars or sugar (hexoses) containing biomass into more economically useful compounds is of increasing interest. Current fuel activities are mainly directed towards ethanol from sugar/glucose. Typically, sucrose and glucose are fermented into ethanol. One glucose molecule is converted into two molecules of ethanol and two molecules of CO2. This conversion has drawbacks especially in view of atom economy, the low energy density of ethanol (7.7 kWh/kg or 6.1 kWh/L) and its relative low boiling point (78.4 degrees Celsius).
Another application area involves the conversion of sugars such as fructose into HMF in the presence of an acid catalyst has been reported (for example in EP0230250 to Suedzucker or EP0561928 to CEA)). In this case, HMF is obtained as a highly potential starting material for obtaining bio-based monomer such as furandicarboxylic acid which can inter alia be used as an alternative to terephthalic acid as a monomer for polyethylene terephthalate type polyesters (Moreau et. al. in Topics in Catalysis Vol 27, Nos. 1-4, 2004, 11-30 and references cited therein). When under these conditions sucrose or glucose was used as a feed, no conversion to HMF is observed (Moreau et. al. in Topics in Catalysis Vol 27, Nos. 1-4, 2004, p 13, col 2. line 2-3), which is a distinct disadvantage given the low price and abundant availability of sucrose and glucose. Only in the presence of DMSO, DMF and DMA (low HMF yields from glucose: Ishida et. al. Bull. Chem. Soc. Jpn 74 2001, 1145) or in a sub- and supercritical mixture of acetone and water (fructose, glucose, sucrose and inulin conversion to HMF in 77%, 48%, 56% and 78% yields respectively: Vogel et. al. Green Chemistry 5, 2003, 280) reasonable HMF yields from starting materials other than fructose were obtained.
In the current market situation, fructose as feed is undesirable given the high price thereof, compared to glucose and/or sucrose. Therefore, so far, no process for the synthesis of HMF has been developed on an industrial scale.
The synthesis chemistry and applications of HMF are reviewed extensively in Lewkowski, ARKIVOC 2001, (i) 17-54; in Gandini, Prog. Polym. Sci. 22, 1997, 1203; in Lichtenthaler, C. R. Chimie, 7, 2004, 65 and Acc. Chem. Res. 35, 2002, 728; and Moreau, Topics in Catalysis, 27, 2004, 11.
Concluding, the current methods for the synthesis of HMF mostly start from fructose and typically do not give high yield, partly attributable to the instability of HMF under the acidic reaction conditions. In most acid-catalysed water-based reactions, the further reaction to levulinic acid and humins has been reported, making this a less attractive alternative.
The present inventors have set out to overcome these disadvantages.